fundal height three cm too small?!?

Leslie • pregnant with #4 xoxo

hi, just recently had a visit with my o.b. was informed my fundal measurements were small( by 3cm) also, my last ultrasound I was told my baby is in the 30 percentage? Although this is my fourth pregnancy I do not feel I know what could be the causes and so on...

just looking a bit of in put, plz.